1999 Civic Hx Mystery surge solved!

[hxman]

Hmm, I guess I'm gonna be on the right lane all the time from now on

I had never seen such high mpg in 3 yrs of driving the car. But my happiness was short lived ... I got a check engine light after driving 314 miles a fillup and another 290miles (600 miles total) on the new o2 sensor. I guess the new o2 sensor isn't good although it seems to be more efficient than my older one. I'll check the codes tomorrow and let you know. I'll probably end up swapping the new o2 sensor back out for the old o2 sensor (that never gave me a CEL) and see if the slow driving does the trick for me.

I'm almost sure the old o2 sensor won't be efficient, so my question is...

What do you think of the NTK 24300 from amazon? Is it something that you consider more reliable? (It is $175)

Thanks,

[hxman]

So the code ended up reading "LEAN"... I suppose the engine is running too lean now, instead. I'll get another NTK 24300 and hope that doesn't produce the CEL again. I hear Denso 234-5052 Air Fuel Ratio Sensor is a good one as well.

[cbaber]

P1164 is the Primary HO2S Circuit Range/Performance problem. I get the same code. Actually I also get P1163 which is Primary HO2S Slow Response. Basically this means that the O2 sensor is not up to the task of reading exhaust gases in wide-band mode. It doesn't mean the car is running lean. There is actually another code for excessive lean and rich conditions.

Do you have an aftermarket exhaust manifold? Your stock one should have the primary O2 sensor right up next to the exhaust ports. I have a theory that modifying the exhaust manifold on these cars can effect lean burn and cause CEL's. My setup places the O2 sensor way back under the car, and I believe this is why I get my CEL. Either that, or the O2 sensor quality is not up to par.

You can still get good mileage with the P1164 code. I've been averaging 46 with the code on all the time. Basically the O2 sensor only malfunctions in lean burn mode, when the engine tries to change the A/F ratio.

[hxman]

Everything in my car is 100% stock or at least OE style. Thanks for letting me know that the engine is not running lean as I was a little concerned about driving it like this. I have already ordered another one from Ebay for $100 (hoping it is better quality this time). Once it arrives I'll test it for another two weeks to see if it's free of CELs.

Alternatively, I could put in my older "lazy" o2 sensor that doesn't ever go into lean burn mode. But I'm in love with lean burn, especially now that I finally got the car to get the promised high mpgs that you guys are getting.

[hxman]

I bought another o2 sensor, a genuine NTK 23400 from ebay that had been listed at $140 for $100 - the seller accepted my best offer and my gamble paid off. I installed that sensor about 5 months ago and I've been getting anywhere from 38 - 42 mpg ever since. In city mpg is more around 36-38 but mixed driving usually gets me about 40 mpg.

I drove only on the highway 60-65 mph the other day and got a sweet 45mpg. On the other hand, if had I driven 80mpg the whole time, I would get around 33-34mpg. What works for me is to keep the rpm around 2500 and keep a light and steady pressure on the gas pedal to stay in lean burn as much as possible.

[California98Civic]

Originally Posted by hxman

I bought another o2 sensor, a genuine NTK 23400 from ebay that had been listed at $140 for $100 - the seller accepted my best offer and my gamble paid off. I installed that sensor about 5 months ago and I've been getting anywhere from 38 - 42 mpg ever since. In city mpg is more around 36-38 but mixed driving usually gets me about 40 mpg.

I drove only on the highway 60-65 mph the other day and got a sweet 45mpg. On the other hand, if had I driven 80mpg the whole time, I would get around 33-34mpg. What works for me is to keep the rpm around 2500 and keep a light and steady pressure on the gas pedal to stay in lean burn as much as possible.

Congrats on getting it running satisfactory. There is still more potential in that car, at freeway cruise. It looks like you might not be in lean burn all that often on the freeway. Aeromods and tire pressure and such will help.